1. Field of the Invention
The present invention relates to toners for use in a color copying machine such as of an electrophotographic type, etc. and, more particularly, to photosensitive microcapsule toners which are cured by exposure to light having a specific wavelength.
2. Description of the Related Art
Conventional copying processes in color copying machines using microcapsules are generally classified into two types: an electrophotographic type and a transfer developing type.
Color copying machines of the electrophotographic type employ microcapsule toners encapsulating an ink component as described in U.S. Pat. Nos. 3,788,994 and 4,016,099; Japanese Patent Publication Nos. Sho 51-35867 and Sho 54-8104; and Japanese Patent Laid-open Nos. Sho 51-132838, Sho 56-119138, Sho 57-202547, Sho 58-153947, Sho 58-176643, Sho 59-170857, Sho 60-57859, Sho 60-227161, Sho 63-32560, and Sho 63-177145.
In such color copying machines, the microcapsule toner is constituted of microcapsule toners of four colors, i.e., yellow, magenta, cyan, and black. These toners are used to form images of these colors on a photosensitive body. Then, the microcapsule toner having such a multicolor image formed on the photosensitive body is transferred onto a recording medium. Then, the recording medium on which the multicolor image has been transferred is heated or pressurized to fix the ink component encapsulated in the microcapsule toner to the recording medium.
On the other hand, color copying machines of the transfer developing type employ microcapsules encapsulating photosensitive resins and coloring matter components as described in U.S. Pat. Nos. 2,548,366, 4,399,209, 4,416,966, and 4,576,891; and Japanese Patent Laid-open Nos. Sho 48-65011, Sho 48-95420, Sho 51-16807, Sho 57-124343, Sho 57-179836, Sho 57-197538, Sho 58-88739, Sho 58-88740, Sho 60-259490, Sho 61-130945, Sho 62-162147, Sho 62-174195, Sho 62-209444, and Sho 62-209531.
In such color copying machines, three kinds of microcapsules encapsulating dye precursors, dyes or pigments of three colors, i.e., yellow, magenta, and cyan are used. These microcapsules have the following characteristics. The microcapsules encapsulating a chromogen for cyan are cured (i.e. rendered solid) by exposure to light having a wavelength of about 650 nm (red light). Microcapsules encapsulating a chromogen for magenta are cured by exposure to light having a wavelength of about 550 nm (green light). Microcapsules encapsulating a chromogen for yellow are cured by exposure to light having a wavelength of about 450 nm (blue light).
These microcapsules are uniformly applied to a carrier sheet to prepare a photosensitive microcapsule coated sheet. The photosensitive microcapsule coated sheet is irradiated with red, green, and blue lights at the same time or separately, thus forming a latent image. Then, the photosensitive microcapsule coated sheet on which the latent image has been formed is heated or pressurized to rupture uncured microcapsules and transfer the encapsulated substance onto a recording medium on which a developer has been coated.
For microcapsule toners of the electrophotographic type mentioned above, four toner tanks are necessary because the toners of four colors are used, causing an increase in cost of the machine. Further, the transfer process to the recording medium is necessarily carried out four times, so that an error in color registering can easily occur.
On the other hand, systems of the transfer developing type have an advantage in that analog exposure can be carried out to thereby reduce the number of steps in the copying process as compared to systems of the electrophotographic type. However, since systems of the transfer developing type need photosensitive microcapsule coated sheets and developer coated recording mediums, these systems consume a large quantity of materials. This causes an increase in running cost. Further, as the photocurable microcapsule coated sheets must be stored in a cool, dark place, it is necessary for a user to secure such a storage place. Similar to a once-through ribbon used for thermal transfer, an unused part of the photosensitive microcapsule coated sheet remains unused, and it is sometimes wasted.
In these circumstances, the present applicant has already proposed in Japanese Laid Open Patent Publication No. Hei 4-249250 a photosensitive microcapsule toner having the features of both types mentioned above. Japanese Laid Open Patent Publication No. Hei 4-249250 discloses a photocurable composition microcapsule toner comprising a radical polymerizable unsaturated group-bearing compound and a metal arene compound as a polymerization initiator and a spectral sensitizing dye.
However, the sensitivity of the photosensitive microcapsule toners proposed above does not fully meet the requirements on recent high-speed machines. In particular, there is a demand for improving the sensitivity of microcapsules which are sensitive to exposure of light having a wavelength of about 650 nm (red light). However, there is a tendency for the improvement in the sensitivity to cause a reduction in temperature and humidity resistance of an image finally formed.